Gray cast iron and cylinder sleeve composed thereof



United States Patent GRAY CAST IRON AND CYLINDER SLEEVE COIWPQSED THEREOF Adna A. Armstrong, Mentor, Ohio, assignor to Thompson Products, Inc. Cleveland, Ohio, a corporation of Ohio No Drawing. Application October 11, 1952, Serial No. 314,409

Claims. (Cl. 148-31) The instant invention relates to an improved method of preparing an article having dimensional stability at high temperatures, and the article resulting therefrom, and more particularly to an improved automotive cylinder sleeve of gray cast iron, and the improved composition thereof and the improved method of making the same.

Articles which are inexpensive to prepare and which have the structural strength of cast iron are in great demand in industry for a number of diiferent purposes, and particularly there is a demand for such articles having dimensional stability at high temperatures. For example, in connection with the particular problem with which the instant invention is principally concerned, namely, the provision of suitable automotive cylinder sleeves, there is a very great need for the provision of such cylinder sleeves that have suitable dimensional stability at the high operating temperatures obtained in the combustion zone in combustion engines such as the diesel engine. it has been found that the cast iron cylinder sleeves heretofore used in certain diesel engines had a tendency to shrink diametrically after a certain period of operation. As will be appreciated, this shrinkage or sleeve collapse results in increased Wear of the sleeve by the ring assembly, and no doubt also results in further overheating of the sleeve by virtue of inefiicient heat transfer from the sleeve to the block. This collapse problem greatly complicated the problem of providing suitable cast iron cylinder sleeves, which otherwise possess a-great number of superior and industrially advantageous properties.

Elaborate studies of this problem have revealed certain differences in collapse properties resulting from casting the iron by different methods, such as sand casting as contrasted to centrifugal casting. Dilierent methods of hardening and tempering or drawing were also investi-- gated; but it appeared that, prior to the instant invention, no one had been able to reach a satisfactory solution to this problem.

The instant invention is based upon the discovery that, by suitable adjustment of the alloying ingredients or additives in a unique manner in cast iron, it is possible to obtain sleeves or the like articles having the properties desired, using industrially acceptable casting, hardening and drawing operations.

It is, therefore, an important object of the instant invention to provide an improved article, cylinder sleeve or the like having dimensional stabilty at high operating temperatures, and to provide an improved composition for and method of preparing such article.

It is a further object of the instant invention to provide an improved method of preparing an article having dimensional stability at high temperatures that comprises melting and then casting a composition of 4:0.4% silicon, 220.3% chromium, 3.25 :05 total carbon, 0.8i0.2% combined carbon, and the remainder iron and incident impurities.

It is another object of the instant invention to provide It is still a further object of the instant invention to.

provide an improved method of preparing automotive cylinder sleeves, that comprises casting to substantially the desired sleeve shape and size a gray cast iron having 3 /z5% silicon, l /22 /2% chromium, the remainder iron and incidental impurities.

It is still another object of the instant invention to provide an improved gray cast iron having substantially the composition: 4i-0.4% silicon, 2i0.3% chromium, 3.25 i0.25% total carbon, 0.8:0.2% combined carbon, and the remainder iron and incidental impurities.

Other and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure of preferred embodiments thereof.

The instant invention consists in, as the most important article embodying the instant invention, an automotive cylinder sleeve composed of gray cast iron having substantially the composition: 3 /25% silicon, l /z-2 chromium, the remainder iron and incidental impurities.

The essence of the instant invention is that the instant 2% Cr-4% Si gray cast iron has unique dimensional stability under the operating conditions ordinarily subjected to automotive cylinder sleeves. As indicated, the amount of silcon employed may range from about 3% to about 5 weight percent, and is preferably about 4 weight percent plus or minus 10% thereof, or 410.4%. (As used herein, the terms parts, percent and mean parts and percent by weight, unless otherwise specified.)

The amount of chromium present in the composition may range from about 1%% to about 2 /2%, and is preferably 220.3%. Heretofore, in the cast irons employed in the production of cylinder sleeves, the amount ofchromium employed, if any, was a relatively small amount being less than about 0.5% in all instances. In some steel compositions, however, substantially greater proportions of chromium have been used for one purpose or another in the so-called high chromium steels, but those skilled in the art will readily recognize that the use of steel generally in connection with cylinder sleeves or the like articles involves an entirely difierent set of problems, and the effectiveness or lack of effectiveness of the use of chromium in a given amount in steel has no relation to the problems here involved in connection with the use of cast iron. As far as the skilled workers in the artwere concerned, there was apparently no particular reason for employing more than the relatively minor amounts of chromium heretofore employed in cast irons adapted to this specific use.

The instant invention, however, resides not only in the unobvious discovery that substantially increasing the chromium content up to about 2% causes a materially significant change in the cast iron properties, but also that the combination of the high chromium content plus approximately twice as great a silicon content results in a uniquely superior composition for the purposes of the instant invention.

. As a rule, silicon (as contrasted to chromium) is present essentially as an impurity in small amounts in all cast irons. Ordinary cast iron seldom contains less than about 0.50% silicon, and on some occasions may contain as much as 3% silicon. As it is generally understood, the silicon probably combines with the iron to form the silicide of iron, which is then dissolved in the balance of the iron. Those skilled in the art have recognized that the influence of silicon on the properties of cast iron is very important, chiefly through its known- Fatented Sept. 4,

rous materials).

apemsbt property of promoting the formation of graphitic carbon, andtherebyin'creasing the softness, and if carried too far, decreasing the strength of the cast iron. Foundry men otter; speak ofsilicon as a softener. Silicon is also understood to influence the decomposition lof iron harbide,..and the presence of some silicon in the carbide tends torender it'less stable. For these, and other reasons,

those skilled in the art have "in most cases attempted to he ep the silicon contents at aminimum, and in the preparation of cast iron cylinder sleeves heretofore" a silicon content appreciably ineircess of 3% was not used, and it was apparently the'general ,attitude that silicon contents in excess thereof should not be used.

It also appears that the generalpractice n hrouiium- J 13 i fi m nP i v vedtm use of chrom um 1 an ints wa meme t i ke -F t The i se ina ion; 'hbw 's i based p h i covery that unigu'ely' superior cast ironcylinder sleeves may be bythe use of a composition having a chromium content substantially in excess of that ordinarily'used in cast iron adapted to this purpose,,a silicon content substantially in circess of that ordinarily used in cast iron adapted tothe instant uses, and a silicon content of twice the chromium content, which is @substantially the reverse of the chromium-silicon proportions heretofore used in cast irons used for cylinder sleeve manufacture (and is also substantially the reverse of the chromium-silicon proportions'used generally infer- Althoirgh it is not desired to jlimit the instant invention to any particular theory or explanation for the superior results obtained --hereby, it is 'belie'ved that there must be some unusual cooperation between the chromium and the silicon so that, among other'thing's, a suitable graphi-te'fiake deposition-is accomplished so that a unique combination of high wear and 'abrasion resistance and high dimensional stabilityunder operatingeondiw tions may beobtained. i i

As :previously mentioned the instant ferrous material is .gray cast iron, which is t-herraine by :which cast irons containing a considerable amount ot the graphitic cai bon are known because of the appearance or their iracture, which is grayish or blackish and coarsely crystalline. In general, such cast irons'may contain fr om-2-vz to about 4% .carbon, as total carbon content, and in the case or the instant invention :the carbon content is preferably 3-.2.5iO.2-5%. The instant cast iron consis'ts ot type 'A' graphite, size 4-13, in a matrix that -is pearli-tic generally in the ?as cast form. .-"l-he .jprimary carbideconten-t is approximately 4-65%. As s=will be explained hereinafter,"

suitable hardening and drawingnhereotresults' in changingrthematrix tto essentia lly a tempered martinsit ic matrix.

As mentioned, in the preferred gray cast iron of the instant invention, the total carbon-content *isabout '3 plus -or minus and the combined jcarboncontent is about 0. 8%, plusonminus 0.2%; remainder bf the composition consists of iron and the incidental impuri-' ties ordinarily present in :c a'st iron.

One of the impurities ordinarily presentin ,cast iron .is

sulfur, which may be presenn'frommere traces tially 0%) to about about 9.1%. Sulfur .in-excess [of the stated maximum amount fimparts undesirable preperties to thecast iron, gun in the practice,of,the instant invention the sulfur content may be about ;Q- 0.1%. 7,

Another impurity ordinarily present :in :cast .iron .is phosphorus. Phosphorus may be present-in substantially trace amounts ('Q% )']1p to about 157;%.-in cast irons..- ln such ,small amounts, the phosphorus present is under? stood toiorm aniron phosphidmgwhioh iis heldin ol tion in the iron. illfLfiI-BOttIttSfiil-ernbout 1.7%;the phosphorus develops =other =.:iuntio ns gin ;the. cast;iron, and the 5 19 :P JQ PH TUS excesslnf that-am n dsno desired in th ins an invention. :Bret'errbly, theiphosk phorps-gcontentqisgquitelow, beiugclessj than about-0.5%

in the cast iron compositions employed in the invention. 7

Still another impurity ordinarily present at least to some extent in cast iron is manganese. Manganese may be present in cast iron in amounts ranging from mere trace amounts to as much as about 2%, and ordinary cast iron usually contains about Oil-2% maganese. in the instant invention, the amount of manganese presen t'may be about 02%, but in some instances it has been found Preferable t employ n ne in ou q 'a (XS-1%, since such relatively small amounts of .manganese' may tendt o impart a slight amount of'additional hardness" to the iron. v p

Other impurities or additives, such as nickel and copper may also be present in small amounts (i. e., 0.5% or less) in the cast iron of the instant invention. e

-As an example of the superior results obtained in the 7 practice of the instant invention, castiron sleeves were made using the compositions 1 and 2 shown in the table below:

Composition 7 The compositions shown in the above table were sand cast in the form of sleeves, and *the general charac'ter of the resulting, cast metallurgical structure obtained in eachcase was that it contained type A,-size [graphite flakes in a pearl'itic matrix. In thecase of composition 1', which embodies-the instant invention, the matrix also contained about 6% oflp'rimary, carbides. The sleeves were hardened by heating to 1550 F. and quenching,"

so as-to obtain an essentially marten's'itic matrix, and a hardness of about 48-50; The sleeves were then drawn or tempered, hyiholding at 600' F. for 'one'hou'r." In the collapse test, the sleeves are maintained for onehour ovenat 600" F; and the decrease in diameter thereof (which is about a five inch diameter) which'tak'es place ,duringrthe heat test isrmeasure'd. As will be-seen' in the instant test, the collapse was .0016 inch for composition ilfanrl ..0025 inch for composition 2, thereby showing that". thecollapse was over 50% greater in the case'pf composition 2, which 'was a composition heretoforeemployed sand casting of cylinder sleeves in standard practice; As another demonstration 'of the superiority of the composition rat the 'instant invention, in this case for purposes of centrifugalcasting, compositions3 and .4,,as shown -helow, were employed in the {centrifugal casting a of isleevessuch vasthose' just described.

The resulting sleeves w'ere hardened vand drawn as. herebe fore described, and' again the collapse testresults indicate the distinct superiority of composition 3,as co'ntrasted to .conipositibnAwhich waslai commercially emsenescence ployed composition for centrifugal casting of cylinder sleeves.

It has also been found that the instant compositions 1 and 3, hereinbefore described, produce cylinder sleeves having superior wear and tear and abrasion resistance and having a much longer operating life during ordinary use.

Again, without limiting the invention to any particular theory, it is believed that the 2% Cr4% Si gray cast iron has the superior results here shown because of a unique cooperation between the hardener," chromium, and the softener, silicon, in these particular proportions, during the casting process. During casting, and particularly sand casting which is preferred for use in the invention, the molten cast iron is poured into the desired shape, and cooling takes place ordinarily at a fairly slow rate so that carbon deposition and flake formation may take place to a suflicient extent to obtain the typical gray cast iron structure.

Unquestionably the instant excessive amount of silicon alone (in the absence of the excessive amount of chromium) would efiect such carbon or graphitic flake deposition as to make the gray cast iron too soft and weak. In contrast, chromium is used in steel and as a hardener for tool steel in amounts of less than 1% and in ball hearings in an amount of less than l /2%. (Chromium in the high-chrome steels functions in a difierent manner metallurgically and is used in amounts of 10, 20 or 30%.) It would appear that the use of chromium in cast iron in amounts in excess of the usual small amount of less than about 0.5% would be wasteful or would result in undue embrittlement of an already brittle material.

Apparently in the instant. casting method, however, the chromium in the high amounts used materially interferes with the tendency of the silicon to cause soft graphitic deposits, to the extent that the chromium substantially overcomes this tendency even for the excessive amount of silicon used; or the chromium in the high amount present forms an appreciable percentage of chromium carbides which cooperate with cementite and for graphite per se to impart additional hardness thereto so as to overcome what would be expected to be the harmful softening efiects of the excessive silicon. Whatever the peculiar phenomenon involved it seems clear that the cooperative co-action or independent actions of the 2% Cr4% Si system take place initially during the casting process so as to obtain a suitable as cast metallurgical structure.

During subsequent use of this cast material, the chromium and silicon must again cooperate; this time the silicon assisting significantly in the dimensional stability of the article and the chromium probably stabilizing the metallurgical structure to overcome any tendency on the part of the silicon to render the carbides (which would now have high amounts of chromium carbides therein) less stable.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. An automotive cylinder sleeve composed of gray cast iron having substantially the composition: EPA-5% silicon, 1%-2%% chromium, the remainder iron and incidental impurities, and having a structure consisting essentially of graphite flakes, and 4-6% primary carbides in a tempered martensitic matrix.

2. A hardened and drawn automotive cylinder sleeve composed of cast iron containing 3%5% silicon, 1 2'-2%% chromium, 26- 1% carbon, 0.810.2 combined carbon, and the principal part of the remainder iron.

3. An automotive cylinder sleeve cast, and then hardened and drawn to obtain an essentially tempered martensitic matrix, from molten cast iron containin 410.4% silicon, 210.3% chromium, 3.251025% carbon, 0-0.1% sulfur, 01.7% phosphorus, 0-2% manganese and the remainder iron.

4. An automotive cylinder sleeve composed of gray cast iron having substantially the composition: 410.4% silicon, 210.3% chromium, 3.251025% total carbon, 0.810.2% combined carbon, and the remainder iron and incidental impurities.

5. Hardened and drawn gray cast iron having a structure of graphite flakes, 4-6% primary carbides and less than 5% free ferrite in essentially a tempered martensitic matrix, and having substantially the composition: 410.4% silicon, 210.3% chromium, 3.251025% carbon, 00.1% sulfur, 0-1.7% phosphorus, 0-2% manganese and the remainder iron.

References Cited in the file of this patent UNITED STATES PATENTS 2,081,304 Moluf May 25, 1937 2,167,301 Jones et al. July 25, 1939 2,287,850 Young June 30, 1942 2,518,055 Olsen et a1 Aug. 8, 1950 

1. AN AUTOMATIVE CYLINDER SLEEVE COMPOSED OF GRAY CAST IRON HAVING SUBSTANTIALLY THE COMPOSITION: 31/2-5% SILICON, 1/2-21/2% CHROMIUM, THE REMAINER IRON AND INCIDENTAL IMPURITIES, AND HAVING A STRUCTURE CONSISTING ESSENTIALLY OF GRAPHITE FLAKES, AND 4-6% PRIMARY CARBIDES IN A TEMPERED MARTENSITIC MATRIX. 